Three point charges, two positive and one negative, each having a magnitude of 20 mC are placed at the vertices of an equilateral triangle (30 cm on a side). What is the magnitude of the electrostatic force on the negative charge?
a. 80 N
b. 40 N
c. 69 N
d. 57 N
e. 75 N
C
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In a short-fiber composite subject to a tensile stress parallel to the fibers, at the center of the fiber the matrix-fiber interface shear stress is equal to _________.
Fill in the blank(s) with the appropriate word(s).
An inventor develops a stationary cycling device by which an individual, while pedaling, can convert all of the energy expended into heat for warming water. How much mechanical energy is required to increase the temperature of 200 g of water (enough for 1 cup of coffee) from 18°C to 94°C? (1 cal = 4.186 J, the specific heat of water is 4 186 J/kg/°C)
a. 6.4E+4 J b. 3.2E+4 J c. 1.6E+4 J d. 1.0E+3 J e. 1.5E+1 J
When we see that a spectral line of a galaxy is broadened, that is, spanning a range of wavelengths, we conclude that
A) we do not have very good resolution of a star's orbital velocity. B) there are many stars traveling at extremely high orbital velocities. C) there are different Doppler shifts among the individual stars in the galaxy. D) we are actually measuring the orbital velocity of a cloud of atomic gas. E) we are actually measuring the orbital velocity of dark matter.
A box slides down a frictionless plane inclined at an angle ? above the horizontal. The gravitational force on the box is directed
A) parallel to the plane in t he same direction as the movement of the box. B) parallel to the plane in the opposite direction as the movement of the box. C) perpendicular to the plane. D) vertically. E) at an angle ? below the inclined plane.